1. Field of Invention
Invention relates to digital signal processing, particularly to electronic image post-processing of video signals to remove blocking artifacts in block-based signals.
2. Description of Background Art
Transform- and block-based coder-decoders or "codecs" are used for digital compression of still or video images (e.g., according to JPEG or MPEG industry standard data or signal format for digital image/video compression). However, when used at relatively low bit rates, such coders produce noticeable coding artifacts, such as blockiness and ringing. Both types of artifacts are undesirable and caused by attenuation of high frequency terms. With blockiness artifact, boundaries of coded blocks are visible in slow-varying regions in image or video frame. In comparison, with ringing artifact, sharp transitions or edges in image cause ringing effect in smooth areas of image. Blockiness is generally the more objectionable of the two artifacts. Although encoder modification may reduce blockiness, such approach would be unacceptable to extent modified encoder does not comply with applicable standards. Accordingly, there is need to reduce blocking artifact, particularly in MPEG-coded video streams, still-images, video conferencing applications, and other transformed-based codecs.